#include <gst/gst.h>

typedef struct {
  GstElement *pipeline;
  GstElement *source;
  GstElement *convert;
  GstElement *resample;
  GstElement *sink;
} CustomData;

//处理pad-add信号
static void pad_added_handler(GstElement *src, GstPad *pad, CustomData *data);

int main(int argc, char *argv[]) {
  CustomData data;
  GstBus *bus;
  GstMessage *msg;
  GstStateChangeReturn ret;
  gboolean terminate = FALSE;

  gst_init(&argc, &argv);

  //创建元素
  data.source = gst_element_factory_make("uridecodebin", "source");
  data.convert = gst_element_factory_make("audioconvert", "convert");
  data.resample = gst_element_factory_make("audioresample", "resample");
  data.sink = gst_element_factory_make("autoaudiosink", "sink");

  //创建空pipeline
  data.pipeline = gst_pipeline_new("test-pipeline");
  if (!data.pipeline || !data.source || !data.convert || !data.resample || !data.sink) {
    g_printerr("Not all elements could be created.\n");
    return -1;
  }

  //构建pipeline, 此时并未连接source元素，稍后会连接
  gst_bin_add_many(GST_BIN(data.pipeline), data.source, data.convert, data.resample, data.sink, NULL);
  if (!gst_element_link_many(data.convert, data.resample, data.sink, NULL)) {
    g_printerr("Elements could not be linked.\n");
    gst_object_unref(data.pipeline);
    return -1;
  }

  //设置播放uri
  g_object_set(data.source, "uri", "https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm", NULL);

  //连接  pad-added 信号
  g_signal_connect(data.source, "pad-added", G_CALLBACK(pad_added_handler), &data);

  //开始播放
  ret = gst_element_set_state(data.pipeline, GST_STATE_PLAYING);
  if (ret == GST_STATE_CHANGE_FAILURE) {
    g_printerr("Unable to set the pipeline to the playing state.\n");
    gst_object_unref(data.pipeline);
    return -1;
  }

  //监听bus
  bus = gst_element_get_bus(data.pipeline);
  do{
    msg = gst_bus_timed_pop_filtered(bus,
    GST_CLOCK_TIME_NONE,
    GST_MESSAGE_STATE_CHANGED | GST_MESSAGE_ERROR | GST_MESSAGE_EOS);

    //处理消息
    if (msg != NULL) {
      GError *err;
      gchar *debug_info;

      switch (GST_MESSAGE_TYPE(msg)) {
      case GST_MESSAGE_ERROR:
          gst_message_parse_error(msg, &err, &debug_info);
          g_printerr("Error received from element %s: %s\n", GST_OBJECT_NAME(msg->src), err->message);
          g_printerr("Debugging information: %s\n", debug_info ? debug_info : "none");
          g_clear_error(&err);
          g_free(debug_info);
          terminate = TRUE;
          break;
      case GST_MESSAGE_EOS:
          g_print("End-of-stream reached.\n");
          terminate = TRUE;
          break;
      case GST_MESSAGE_STATE_CHANGED:
          if (GST_MESSAGE_SRC (msg) == GST_OBJECT (data.pipeline)) {
            GstState old_state, new_state, pending_state;
            gst_message_parse_state_changed (msg, &old_state, &new_state, &pending_state);
            g_print ("Pipeline state changed from %s to %s:\n",
                gst_element_state_get_name (old_state),
                gst_element_state_get_name (new_state)
            );
          }
          break;
          default:
              g_print("Unexpected message received.\n");
              break;
      }

      gst_message_unref (msg);
    }
  }while(!terminate);

  //释放资源
  gst_object_unref(bus);
  gst_element_set_state(data.pipeline, GST_STATE_NULL);
  gst_object_unref(data.pipeline);
  return 0;
}

//pad-added处理函数
static void pad_added_handler(GstElement *src, GstPad *new_pad, CustomData *data) {
  GstPad *sink_pad = gst_element_get_static_pad(data->convert, "sink");
   GstPadLinkReturn ret;
   GstCaps *new_pad_caps = NULL;
   GstStructure *new_pad_struct = NULL;
   const gchar *new_pad_type = NULL;

   g_print("Received new pad '%s' from '%s':\n", GST_PAD_NAME(new_pad), GST_ELEMENT_NAME(src));

    // 已经连接, 退出
    if (gst_pad_is_linked (sink_pad)) {
      g_print ("We are already linked. Ignoring.\n");
      goto exit;
    }

    // 获取pad的caps
    new_pad_caps = gst_pad_get_current_caps (new_pad);
    new_pad_struct = gst_caps_get_structure (new_pad_caps, 0);
    new_pad_type = gst_structure_get_name (new_pad_struct);
    if (!g_str_has_prefix (new_pad_type, "audio/x-raw")) {
      g_print ("It has type '%s' which is not raw audio. Ignoring.\n", new_pad_type);
      goto exit;
    }

    // !!! 连接pad !!!
    ret = gst_pad_link (new_pad, sink_pad);
    if (GST_PAD_LINK_FAILED (ret)) {
      g_print ("Type is '%s' but link failed.\n", new_pad_type);
    } else {
      g_print ("Link succeeded (type '%s') in pad_added_handler.\n", new_pad_type);
    }

  exit:
    // 释放caps
    if (new_pad_caps != NULL)
      gst_caps_unref (new_pad_caps);

    // 释放sink pad
    gst_object_unref (sink_pad);
}
